-. 964 NATURE AND LIFE. +x 
too, the panspermist theory, neglected and ignored since 
the time of its earliest authors—among whom Astier, in 
1813, deserves particular mention—has only been definitely 
established in our time, through the experiments made by 
Pasteur. That famous chemist has improved a vague 
sketch into a finished and masterly drawing. These experi- 
ments, repeated and varied in a thousand ways, all refer to 
the investigation, by comparison, of what takes place in the 
same fermentable liquid, under the different conditions of 
exposure to common air, filled with dust, and of con- 
tact with purified air. For instance, Pasteur puts a cer- 
tain quantity of a liquid, that readily undergoes change, 
into glass balls through which a current of air may be 
made to pass. Fermentation and the development of small 
organisms take place very soon in the balls through which 
common air circulates; but, if the air, before entering them, 
passes through a plug of cotton, no change in the liquid is 
observed. When the volume of air, thus filtered through 
cotton, is considerable, the plug is so filled with dust as 
“to turn black. Now, this dust, in addition to a quantity 
of mineral particles, and fluff of many kinds, contains spores 
and germs of fermenting substance, as is proved by the 
fact that the smallest quantity of it, sprinkled in pure liquid, 
will produce fermentation in it. An experiment of another 
kind is this: Pasteur, by an ingenious arrangement, inserts 
and withdraws from a glass jar, filled with pure air, the 
juice from the inside of a single grape, so that, during the 
experiment, the juice communicates neither with the surface - 
of the grape nor with the atmospheric air. The juice, 
thus obtained, shows no trace of fermentation, remaining 
unchanged as long as the jar is closed; but if it is opened, 
or if its contents are mixed with a few drops of water in 
which the surface of the grape has been washed, fermenta- 
tion is set up in it at once. This is because the outside of 
grapes is always covered with yeast-germs, even when the 
